[PATCH] net: mlx5: remove pointless memcpy

[PATCH] net: mlx5: remove pointless memcpy

[Arnd Bergmann]

gcc-8 notices that the memcpy in mlx5_core_query_xsrq() makes no
sense because the source and destination variables are identical:

drivers/net/ethernet/mellanox/mlx5/core/transobj.c: In function 'mlx5_core_query_xsrq':
drivers/net/ethernet/mellanox/mlx5/core/transobj.c:347:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]

Either one of the pointers should be something else, or the code is
completely bogus. Removing the memcpy() won't change the behavior
but gets rid of the warning.

Fixes: 01949d0109ee ("net/mlx5_core: Enable XRCs and SRQs when using ISSI > 0")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Please review carefully, I have no idea what the author actually
intended here.
---
 drivers/net/ethernet/mellanox/mlx5/core/transobj.c | 8 --------
 1 file changed, 8 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/transobj.c b/drivers/net/ethernet/mellanox/mlx5/core/transobj.c
index 9e38343a951f..75450f7d53bf 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/transobj.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/transobj.c
@@ -332,20 +332,12 @@ int mlx5_core_destroy_xsrq(struct mlx5_core_dev *dev, u32 xsrqn)
 int mlx5_core_query_xsrq(struct mlx5_core_dev *dev, u32 xsrqn, u32 *out)
 {
 	u32 in[MLX5_ST_SZ_DW(query_xrc_srq_in)] = {0};
-	void *srqc;
-	void *xrc_srqc;
 	int err;
 
 	MLX5_SET(query_xrc_srq_in, in, opcode,   MLX5_CMD_OP_QUERY_XRC_SRQ);
 	MLX5_SET(query_xrc_srq_in, in, xrc_srqn, xsrqn);
 	err = mlx5_cmd_exec(dev, in, sizeof(in), out,
 			    MLX5_ST_SZ_BYTES(query_xrc_srq_out));
-	if (!err) {
-		xrc_srqc = MLX5_ADDR_OF(query_xrc_srq_out, out,
-					xrc_srq_context_entry);
-		srqc = MLX5_ADDR_OF(query_srq_out, out, srq_context_entry);
-		memcpy(srqc, xrc_srqc, MLX5_ST_SZ_BYTES(srqc));
-	}
 
 	return err;
 }
-- 
2.9.0

Re: [PATCH] net: mlx5: remove pointless memcpy

[Jason Gunthorpe]

On Fri, Feb 02, 2018 at 04:46:30PM +0100, Arnd Bergmann wrote:
> gcc-8 notices that the memcpy in mlx5_core_query_xsrq() makes no
> sense because the source and destination variables are identical:
> 
> drivers/net/ethernet/mellanox/mlx5/core/transobj.c: In function 'mlx5_core_query_xsrq':
> drivers/net/ethernet/mellanox/mlx5/core/transobj.c:347:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]
> 
> Either one of the pointers should be something else, or the code is
> completely bogus. Removing the memcpy() won't change the behavior
> but gets rid of the warning.
> 
> Fixes: 01949d0109ee ("net/mlx5_core: Enable XRCs and SRQs when using ISSI > 0")
> Signed-off-by: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
> Please review carefully, I have no idea what the author actually
> intended here.

I think they intended to adjust the command return between
mlx5_ifc_query_srq_out_bits and mlx5_ifc_query_xrc_srq_out_bits?

> index 9e38343a951f..75450f7d53bf 100644
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/transobj.c
> @@ -332,20 +332,12 @@ int mlx5_core_destroy_xsrq(struct mlx5_core_dev *dev, u32 xsrqn)
>  int mlx5_core_query_xsrq(struct mlx5_core_dev *dev, u32 xsrqn, u32 *out)
>  {
>  	u32 in[MLX5_ST_SZ_DW(query_xrc_srq_in)] = {0};
> -	void *srqc;
> -	void *xrc_srqc;
>  	int err;
>  
>  	MLX5_SET(query_xrc_srq_in, in, opcode,   MLX5_CMD_OP_QUERY_XRC_SRQ);
>  	MLX5_SET(query_xrc_srq_in, in, xrc_srqn, xsrqn);
>  	err = mlx5_cmd_exec(dev, in, sizeof(in), out,
>  			    MLX5_ST_SZ_BYTES(query_xrc_srq_out));
> -	if (!err) {
> -		xrc_srqc = MLX5_ADDR_OF(query_xrc_srq_out, out,
> -					xrc_srq_context_entry);
> -		srqc = MLX5_ADDR_OF(query_srq_out, out, srq_context_entry);
> -		memcpy(srqc, xrc_srqc, MLX5_ST_SZ_BYTES(srqc));
> -	}

Probably should add a

BUILD_BUG_ON(MLX5_BYTE_OFF(query_xrc_srq_out, xrc_srq_context_entry) == MLX5_BYTE_OFF(query_srq_out, srq_context_entry));

Just for clarity that the SRQ and XRC_SRQ are being used interchangeably.

and the 'err' variable can be eliminated.

Curious though that I can't find a call site for it, and removing the
prototype doesn't break the build.. Seems like dead code.

Jason
--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] net: mlx5: remove pointless memcpy

[Arnd Bergmann]

On Fri, Feb 2, 2018 at 8:06 PM, Jason Gunthorpe <jgg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> wrote:
> On Fri, Feb 02, 2018 at 04:46:30PM +0100, Arnd Bergmann wrote:
>> gcc-8 notices that the memcpy in mlx5_core_query_xsrq() makes no
>> sense because the source and destination variables are identical:
>>
>> drivers/net/ethernet/mellanox/mlx5/core/transobj.c: In function 'mlx5_core_query_xsrq':
>> drivers/net/ethernet/mellanox/mlx5/core/transobj.c:347:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]
>>
>> Either one of the pointers should be something else, or the code is
>> completely bogus. Removing the memcpy() won't change the behavior
>> but gets rid of the warning.
>>
>> Fixes: 01949d0109ee ("net/mlx5_core: Enable XRCs and SRQs when using ISSI > 0")
>> Signed-off-by: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
>> Please review carefully, I have no idea what the author actually
>> intended here.
>
> I think they intended to adjust the command return between
> mlx5_ifc_query_srq_out_bits and mlx5_ifc_query_xrc_srq_out_bits?
>
>> index 9e38343a951f..75450f7d53bf 100644
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/transobj.c
>> @@ -332,20 +332,12 @@ int mlx5_core_destroy_xsrq(struct mlx5_core_dev *dev, u32 xsrqn)
>>  int mlx5_core_query_xsrq(struct mlx5_core_dev *dev, u32 xsrqn, u32 *out)
>>  {
>>       u32 in[MLX5_ST_SZ_DW(query_xrc_srq_in)] = {0};
>> -     void *srqc;
>> -     void *xrc_srqc;
>>       int err;
>>
>>       MLX5_SET(query_xrc_srq_in, in, opcode,   MLX5_CMD_OP_QUERY_XRC_SRQ);
>>       MLX5_SET(query_xrc_srq_in, in, xrc_srqn, xsrqn);
>>       err = mlx5_cmd_exec(dev, in, sizeof(in), out,
>>                           MLX5_ST_SZ_BYTES(query_xrc_srq_out));
>> -     if (!err) {
>> -             xrc_srqc = MLX5_ADDR_OF(query_xrc_srq_out, out,
>> -                                     xrc_srq_context_entry);
>> -             srqc = MLX5_ADDR_OF(query_srq_out, out, srq_context_entry);
>> -             memcpy(srqc, xrc_srqc, MLX5_ST_SZ_BYTES(srqc));
>> -     }
>
> Probably should add a
>
> BUILD_BUG_ON(MLX5_BYTE_OFF(query_xrc_srq_out, xrc_srq_context_entry) == MLX5_BYTE_OFF(query_srq_out, srq_context_entry));
>
> Just for clarity that the SRQ and XRC_SRQ are being used interchangeably.
>
> and the 'err' variable can be eliminated.
>
> Curious though that I can't find a call site for it, and removing the
> prototype doesn't break the build.. Seems like dead code.

I checked the git history and don't see any user ever added after the function
first showed up in the kernel, same for a couple of other functions from
commit 01949d0109ee ("net/mlx5_core: Enable XRCs and SRQs when
using ISSI > 0").

Can you come up with a proper patch for this isse, either removing the
dead code, or fixing it appropriately? You clearly understand what this
file is about, and I don't ;-)

      Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [PATCH] net: mlx5: remove pointless memcpy

[Saeed Mahameed]

On 02/02/2018 12:26 PM, Arnd Bergmann wrote:
> On Fri, Feb 2, 2018 at 8:06 PM, Jason Gunthorpe <jgg-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org> wrote:
>> On Fri, Feb 02, 2018 at 04:46:30PM +0100, Arnd Bergmann wrote:
>>> gcc-8 notices that the memcpy in mlx5_core_query_xsrq() makes no
>>> sense because the source and destination variables are identical:
>>>
>>> drivers/net/ethernet/mellanox/mlx5/core/transobj.c: In function 'mlx5_core_query_xsrq':
>>> drivers/net/ethernet/mellanox/mlx5/core/transobj.c:347:3: error: 'memcpy' source argument is the same as destination [-Werror=restrict]
>>>
>>> Either one of the pointers should be something else, or the code is
>>> completely bogus. Removing the memcpy() won't change the behavior
>>> but gets rid of the warning.
>>>
>>> Fixes: 01949d0109ee ("net/mlx5_core: Enable XRCs and SRQs when using ISSI > 0")
>>> Signed-off-by: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
>>> Please review carefully, I have no idea what the author actually
>>> intended here.
>>
>> I think they intended to adjust the command return between
>> mlx5_ifc_query_srq_out_bits and mlx5_ifc_query_xrc_srq_out_bits?
>>
>>> index 9e38343a951f..75450f7d53bf 100644
>>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/transobj.c
>>> @@ -332,20 +332,12 @@ int mlx5_core_destroy_xsrq(struct mlx5_core_dev *dev, u32 xsrqn)
>>>  int mlx5_core_query_xsrq(struct mlx5_core_dev *dev, u32 xsrqn, u32 *out)
>>>  {
>>>       u32 in[MLX5_ST_SZ_DW(query_xrc_srq_in)] = {0};
>>> -     void *srqc;
>>> -     void *xrc_srqc;
>>>       int err;
>>>
>>>       MLX5_SET(query_xrc_srq_in, in, opcode,   MLX5_CMD_OP_QUERY_XRC_SRQ);
>>>       MLX5_SET(query_xrc_srq_in, in, xrc_srqn, xsrqn);
>>>       err = mlx5_cmd_exec(dev, in, sizeof(in), out,
>>>                           MLX5_ST_SZ_BYTES(query_xrc_srq_out));
>>> -     if (!err) {
>>> -             xrc_srqc = MLX5_ADDR_OF(query_xrc_srq_out, out,
>>> -                                     xrc_srq_context_entry);
>>> -             srqc = MLX5_ADDR_OF(query_srq_out, out, srq_context_entry);
>>> -             memcpy(srqc, xrc_srqc, MLX5_ST_SZ_BYTES(srqc));
>>> -     }

OMG!

>>
>> Probably should add a
>>
>> BUILD_BUG_ON(MLX5_BYTE_OFF(query_xrc_srq_out, xrc_srq_context_entry) == MLX5_BYTE_OFF(query_srq_out, srq_context_entry));
>>
>> Just for clarity that the SRQ and XRC_SRQ are being used interchangeably.
>>
>> and the 'err' variable can be eliminated.
>>
>> Curious though that I can't find a call site for it, and removing the
>> prototype doesn't break the build.. Seems like dead code.
> 
> I checked the git history and don't see any user ever added after the function
> first showed up in the kernel, same for a couple of other functions from
> commit 01949d0109ee ("net/mlx5_core: Enable XRCs and SRQs when
> using ISSI > 0").
> 
> Can you come up with a proper patch for this isse, either removing the
> dead code, or fixing it appropriately? You clearly understand what this
> file is about, and I don't ;-)

Simply this is just pointless dead code, will remove it, there is no point of trying to
figure out what the author was thinking the day he wrote that patch :)

Thank you Arnd for spotting this.

> 
>       Arnd
> 
--
To unsubscribe from this list: send the line "unsubscribe linux-rdma" in
the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html